I am fairly new at this...

I just can't figure out why it would make a difference if the case mouth lines up exactly with a cannelure or not. Is the reason one of safety, or accuracy?

Thanks,
Todd

It depends on the application,,,If you're shooting hot pistol loads,It helps keep the remaining bullets seated.Winchester highly reccomends it when using 296 in magnum loads.Some people reccomend when loading for auto's so the bullet has less of a chance to be pushed bach into the case when the action is cycled.I prefer a taper crimp vs. a roll crimp for all my loads.As far as the cannulre, I use it for my revolver loads,but not nescessarily for my rifles

If you are using lead bullets, you can crimp just about anywhere you please. If you are using jacketed bullets, you will buckle your cases if you try to crimp anywhere except in a crimping groove on the bullet!! The bullet jacket is too tough to allow a crimp to be put just anywhere, and your case mouth has no place toi go!! Ruined case!!

Also, NEVER crimp unless you have to. Only revolver loads, and loads that are to be used in tubular magazines, or HEAVY-RECOILING calibers (.416 Rigby up) need to be routinely crimped.

If you crimp in the cannelure, it will lock the bullet in the case and will not move. A cannelure also provides the space that is needed for the lip of the case to be rolled into when using a roll crimp.
I have found that I get much less velocity variation when crimping. The best tool is a Lee Factory Crimp die. You cannot buckle cases with it unlike the roll crimp in most reloading dies.
I have and use the Lee die in .22-250, 6mm, .338 win, .348, .416 Dakota and .450AK. If you have a wildcat or a non listed cartridge, for $25.00 and a dummy case with bullet, Lee will make one for you. Check their website http://www.leeprecision.com/catalog/browse.cgi?1022934332.3957=dies-p3.html
Lee will make a die for any case that is .580" or smaller measured .20" above the rim.

Thanks for the replies.

I actually am thinking of crimping for a 416 Taylor in which I (regretfully) used the standard, too short Mauser mag box.

What prompted the question was the fact that the cannelure is a "far bit" from the case mouth in my loads. I use the Hornady 400 gr RN, and load to COL of ~3.3" If I shoved the bullet down to get the cannelure at the case mouth, I'm not sure where pressures would be.

Hmmm.

Todd